"1. The serpentine and pyroxene which fill the cavities of the calcareous matter have no appearance of concretionary structure. On the contrary, their aspect is that of matter introduced by infiltration, or as sediment, and filling spaces previously existing. In other words, the calcareous matter has not been moulded on the forms of the serpentine and augite, but these have filled spaces or chambers in a hard calcareous mass. This conclusion is further confirmed by the fact, to be referred to in the sequel, that the serpentine includes multitudes of minute foreign bodies, while the calcareous matter is uniform and homogeneous. It is also to be observed that small veins of carbonate of lime occasionally traverse the specimen's, and in their entire absence of structures other than crystalline, present a striking contrast to the supposed fossils. "2. Though the calcareous laminæ have in places a crystalline cleavage, their forms and structures have no relation to this. Their cells and canals are rounded, and have smooth walls, which are occasionally lined with films apparently of carbonaceous matter. Above all, the minute tubuli are different from anything likely to occur in merely crystalline calc-spar. While in such rocks little importance might be attached to external forms simulating the appearances of corals, sponges, or other organisms, these delicate internal structures have a much higher claim to attention. Nor is there any improbability in the preservation of such minute parts in rocks so highly crystalline, since it is a circumstance of frequent occurrence in the microscopic examination of fossils that the finest structures are visible in specimens in which the general form and the arrangement of parts have been obliterated. It is also to be observed that the structure of the calcareous laminæ is the same, whether the intervening spaces are filled with serpentine or with pyroxene. "3. The structures above described are not merely definite and uniform, but they are of a kind proper to animal organisms, and more especially to one particular type of animal life, as likely as any other to occur under such circumstances: I refer to that of the Rhizopods of the order Foraminifera. The most important point of difference is in the great size and compact habit of growth of the specimens in question; but there seems no good reason to maintain that Foraminifera must necessarily be of small size, more especially since forms of considerable magnitude referred to this type are known in the Lower Silurian. Professor Hall has described specimens of Receptaculites twelve inches in diameter; and the fossils from the Potsdam formation of Labrador, referred by Mr. Billings to the genus Archæocyathus, are examples of Protozoa with calcareous skeletons scarcely inferior in their massive style of growth to the forms now under consideration.